I've just received trade offer from Endorlight game which used different combinations of classID/instanceID for the same items, such as <1450080555, 246376127> and <1450080555, 0> for Birdy trading card.
This is the first time I've seen something like that, as up to this point all classID + instanceID matched nicely. It's not good because it results in possibly wrong results regarding numbers of the same cards.
It's not any major problem scamming-wise, as ASF does other checks (including appID checks) so in worst case we could accept a trade that is not neutral+ for us, such as 1 -> 2 dupes one.
This commit fixes wrong logic for that particular trade I've encountered, and many similar ones, but I have no idea if we can really base key on classID only.
Number seems big enough to fit all steam items, but if there ever happens item that will have same classID as other one, we'll be in deep sh*t.
I ran a test on my Steam account with 7.5k+ items and didn't find any item which could cause such conflict, so I can at least assume that the issue doesn't exist for majority of Steam users.
Sadly there doesn't seem to be any good way to solve it either, as if such conflicts happens, then we will have 3 items such as <7, 1>, <7, 4> and <7, 0>. We can't know if 0 should be 1 or 4 (thanks GabeN).
This seems to be best solution for that problem, and until we find clasID conflict, we can sleep in peace.
